Many techniques have been utilized to provide a soundtrack for a motion picture. One technique uses a magnetic medium similar to that used for magnetic recording tape. A soundtrack is then formed by applying the magnetic medium onto a motion picture filmstrip. However, this technique has disadvantages. A disadvantage is that the recording medium does not adhere well to the filmstrip. This results in a relatively short film life. In addition, the recording medium typically used is abrasive, which erodes and degrades the magnetic playback head, thus rendering it inoperable.
Another technique includes the formation of an analog optical sound recording on the filmstrip. One such recording is known as a variable area recording. This type of recording provides a soundtrack having optically translucent or opaque areas whose width varies according to the instantaneous amplitude of the sound. During movie projection, the soundtrack is illuminated from behind by a lamp and is viewed in front through a slit by a photocell. As the filmstrip advances, the photocell receives an amount of light that varies in accordance with the varying width of the varying translucent or opaque areas of the soundtrack. The photocell produces a corresponding voltage which is then utilized to reproduce the sound. However, this type of soundtrack also has disadvantages. A disadvantage is that the characteristics of the translucent or opaque areas may change due to factors such as contaminants or surface scratches on the filmstrip resulting in noise or other sound degradation.
In another type of optical recording, a soundtrack is configured such that it conforms to a curve that is empirically derived to provide the best compromise between signal to noise ratio, dynamic range and frequency response. This type of soundtrack is known in the art as the "Academy" soundtrack. As is well known, however, the Academy soundtrack has disadvantages since it is only monophonic, has a relatively low signal to noise ratio and relatively high distortion.
Digital optical recordings have also been used to provide a soundtrack. Generally, such recordings are formed by converting analog sound signals to digital sound signals. A filmstrip is then exposed to light which is modulated in accordance with the digital sound signals to form a digital soundtrack on the filmstrip. Digital soundtracks have many advantages. One advantage is increased resistance to audible degradation caused by repeated use. In addition, digital soundtracks substantially reduce the amount of hiss and noise associated with analog soundtracks. As such, an increasing number of motion pictures include a digital optical soundtrack.
However, many movie theaters are not equipped to reproduce a digital optical soundtrack. Consequently, it is desirable to provide a motion picture having a standard analog optical soundtrack and a digital optical soundtrack. This would insure compatibility with theaters having either analog or digital sound reproduction systems. In this regard, reference is made to U.S. Pat. No. 4,306,781 entitled MULTI-CHANNEL SOUND AND DATA SYSTEM which issued on Dec. 22, 1981 to Mosely. This patent discloses a multi purpose sound/data system for motion picture film. As described therein, this system is capable of recording and reproducing digital and/or analog data such that there is no interference between different information channels.
U.S. Pat. No. 4,600,280 entitled DIGITAL AUDIO RECORDING/PLAYBACK SYSTEM FOR MOTION PICTURE FILM which issued to Clark on Jul. 15, 1986 describes a configuration for a filmstrip having digital and analog soundtracks. In this configuration, the filmstrip includes a three channel digital soundtrack extending along the length of filmstrip between the right sprocket holes and the picture frames. In addition, the film strip includes two conventional variable area soundtracks positioned between the left sprocket holes and the picture frames.
In addition, PCT Application WO 92/14239, entitled STORAGE MEDIUM AND APPARATUS AND METHOD FOR RECOVERING INFORMATION FROM SUCH MEDIUM BY OVERSAMPLING published Aug. 20, 1992 describes an alternate configuration for a filmstrip having analog and digital soundtracks. This application describes a filmstrip having two conventional analog stereo variable area soundtracks which are positioned in conventional locations on the film strip. In this application, however, a digital soundtrack is positioned between the sprocket hole perforations on both sides of the film strip. Alternatively, a digital soundtrack may be positioned on the edges of the film. Furthermore, the digital soundtrack may include both the area between the perforations and the edges of the film strip.
A motion picture may be manufactured by utilizing a contact printing process in a manner well known in the art. In this process, a sound negative having a negative analog optical soundtrack and a picture negative are processed by a contact printer to form a positive print. The addition of a negative digital optical soundtrack to a sound negative having a negative analog optical soundtrack is well known in the art. Standard contact printers have been modified in order to utilize such sound negatives to form digital and analog soundtracks on a filmstrip. In this regard, reference is made to an article entitled DOLBY STEREO SR-D published by Dolby Laboratories Inc. in 1991. This article generally discloses the addition of a mechanical assembly to a laboratory printer that enables the printing of a digital optical soundtrack on a positive print without using special print film.
However, it is known in the art that this mechanical assembly is complex because of its location on the printer. As such, the mechanical assembly is difficult to use and expensive to fabricate. In addition, the mechanical assembly utilizes sprockets for advancing the print film and the sound negative. It is known that sprockets cause damage on portions of the print film and sound negative that are located adjacent to the sprocket holes. Such damage may prevent a substantial portion of a soundtrack adjacent to the sprocket holes from being correctly formed on the print film and accurately read by sound reproducing equipment. Therefore, there is a need in the art for a mechanical assembly for a contact printer that enables the printing of a digital optical soundtrack that is inexpensive to fabricate, relatively easy to use and causes negligible wear of the print film and sound negative.